When selecting a PTO, the operating conditions, such as the torque to be transmitted, the engine speed, the direction of rotation of the engine, the duration and frequency of operation, play an important role, as do the occurrence of fluctuating (peak) loads, vibrations and high initial torques.

Another important criterion is whether or not the PTO can or may be clutch-dependent. For gearbox PTO's are often preferred because of their price, location and the large number of ratios, which makes them suitable for many applications. DAF also offers engine-dependent PTO's, with connections to the crankshaft on the front (front-end PTO), or to the flywheel housing at the rear (DAF engine PTO or ZF/NMV). An engine-PTO is clutch-independent and is mostly used to drive auxiliary units that are operated during driving or shunting. In this section, both PTO types will be dealt with.

If the auxiliary consumer requires high torques, it should be checked whether the engine is capable of delivering the power required at the speed specified. The loss of efficiency between the engine and the auxiliary consumer should also be taken into account.

Finally, various versions are available with an output DIN flange or a pump connection, suitable for direct mounting of a hydraulic pump according to ISO standard 7653 (type D).

Engine and driveline must not be impeded in their movements as a result of the installation of a PTO and the auxiliary consumers driven by it.

Conditions for use

Engaging of in particular gearbox PTO's should be done while the vehicle is stationary and the engine running at idling speed. After depressing the clutch pedal, wait about 2 to 3 seconds until the gearbox countershaft has fully stopped moving, before engaging the PTO. Gear wheel rattle should always be avoided. After engine speed has been increased to 1000 rpm, you can slowly release the clutch pedal. Minimum engine speed, MX and PR, during PTO operation: 800 rpm, FR and GR engines 1000 rpm.

Vehicles with an AS-Tronic gearbox have an electronic controlled (automatic) engaging procedure which operates according a factory or customer defined parameter setting (software).

Permissible power take off for engine PTOs in combination with an AS-Tronic gearbox is 10% of the engine power with a maximum of 32kW. For engine PTOs in combination with AS-Tronic Lite gearboxes, DAF Sales Engineering should be consulted.

As soon as the PTO and pump have definitively been selected, the maximum power take-off can be calculated on the basis of the torque and power calculation. PTO's can roughly be divided into three classes, namely light, medium and heavy, for short-lasting or intermittent use to continuous operation. See the table below.

Extremely high initial torques, due, for example, to the mass inertia of the driven equipment.

Protection

The maximum take-off torques specified for the PTO's supplied by DAF, are based on uniform (vibration-free, non-shock) loads without the occurrence of axial forces. The maximum initial torques must never be higher than 2 times the value specified in the gearbox PTO specifications. For the engine PTO a 15% torque increase is accepted.If higher torques may occur, an overload protection device must be mounted in the driveline, in the form of a slipping clutch or a security flange. Furthermore, the clutch should have extra protection to prevent the PTO from being engaged too early. With such protection, the clutch pedal must be fully engaged before PTO operation is enabled. According to the cut-in conditions of the VIC (see section 7.21: 'PTO control/protection'), the VIC only checks whether the clutch pedal has been 'touched' or not. If an N/10 PTO is ordered ex-works, the full clutch protection is always included. N/10 PTOs as available on ZF gearboxes fitted to LF & CF65 do not have the feature of Clutch Protection available. Further information can be obtained from DAF.

For the ZF gearbox PTO's the maximum torque specifications in the overviews have been calculated at a PTO speed of 1500 rpm for a nominal service life of 500 hours.

Oil temperature

During prolonged PTO operation, the gearbox oil temperature must not rise above 110°C. Temperatures up to 130°C are permissible for brief periods (max. 30 minutes). If necessary (check to be sure!), an extra oil cooler should be fitted on the gearbox. In such cases, consult DAF.

Torque and output calculation

- PTO selection

To be able to select the right PTO, it is necessary to calculate the drive torque (I) on the basis of the desired PTO speed (II) and the required effective output (III), assuming that these data of the driven equipment are known:

- Pump selection

For the selection of the right pump for a hydraulic drive, it is first important to determine the effective pump output (Pe) on the basis of the required pump delivery (IV), the system operating pressure (V) and the efficiency (III). Subsequently, the PTO drive torque (I) can be calculated for the selection of the PTO on the basis of the above-mentioned data:

Where:

npto

=

rpm of power take off unit

[min-1]

nengine

=

rpm of truck engine

[min-1]

rev

=

revolution of hydraulic pump shaft

i

=

PTO reduction ratio

[-]

M

=

PTO drive torque

[Nm]

Pn

=

calculated nominal output

[kW]

Pe

=

required effective output

[kW]

C

=

specific pump capacity

[cm3/rev]

Q

=

actually required delivery

[l/min]

p

=

hydraulic system operating pressure

[bar]

η

=

efficiency: η = η 1x η 2x η 3x...etc.

[-]

Speed Factor

If the calculated load is higher than the maximum permissible load, sometimes a lower-capacity pump is specified. By using a higher-speed PTO with a higher speed factor, and/or a higher engine speed, in general the same delivery and power take-off can be realised, however at a proportionally lower PTO drive torque.

Direct pump mounting

For all gearbox PTO applications where the pump is flange-mounted on the PTO, the following limitation applies, unless stated otherwise in the PTO overviews:

The static moment resulting from the pump weight on the both pump connections on the N.../10 PTO mating surface should in general not exceed 30 Nm. For the ZF PTO, types NL/1c, NL/10c, NH/1c, NL/4c and NH/4c the maximum permissible static moment is 50 Nm.

The static moment for the Hydrocar P2264 and 81Z2 PTO's is 50Nm, for the P2264 the static monent is 20Nm.

The maximum static moment resulting from the pump weight on the DAF PR and MX Engine PTO mating surface is 40 Nm. Allison gearboxes the maximum allow a static moment of 40 Nm. For the LF and CF65 Series the bending moment on the engine PTO housing should not exceed 45 Nm.

If the PTO device generates a larger bending moment than allowed it should be supported by additional mounting brackets or remote mounted elsewhere and driven by a carden shaft.

In some cases, the pump dimensions prove to be restricted by the diameter of the drive flange in combination with the location of the countershaft in the gearbox (which determines the location of the PTO). The clearance between pump and drive flange (or shaft) should therefore always be checked.

Maximum torque on direct pump connection

Incorrect use of the hydraulic system (for instance at unduly high revs) may cause damage to the hydraulic pump and subsequently to the gearbox.

The pump shaft should therefore be provided with a high temperature-resistant double seal, with a bleed hole between the two seals, to prevent gearbox oil being sucked in or hydraulic oil getting into the gearbox. Note: this is one of the reasons why DAF no longer uses ZF PTO type N/2c!

In some cases the mounting of a so-called pump adapter is recommended. This adapter is provided with a separate PTO seal and a bleed hole (take note of the higher static moment). The ZF N../4 PTO has a separate pump bearing, so that in that case the mounting of an adapter is not necessary. At any rate, the pump supplier's instructions should always be consulted.

Drive shafts

The angles formed by the drive shaft couplings between PTO and auxiliary consumer should be equal to each other and should not exceed the following maximum values:

maximum of 6 degrees for front-end PTO's

maximum of 8 degrees for all other PTO's

The shafts must be installed in such a way that uniform running of the driven equipment is ensured. This calls for a Z or W arrangement of the shafts. Excessively large drive shaft angles or PTO drive resonance may cause serious vibration far above the calculated (nominal) torques. In case of doubt, tests should always be made before a particular application can be guaranteed.

When the shaft angles (α1 and α2) differ from each other, non-uniformity (α R) will be higher than in the optimum situation, when α1= α2. Non-uniformity can be calculated with the formula:

where αR (permissible) ≤ 3°.

Z arrangement

W arrangement

The tools represented by the opposite drawings can be used for the correct alignment of the drive shafts. The sliding joint of the drive shaft on the gearbox should permit a forward movement of at least 8 mm and a rearward movement of at least 5 mm.

Ensure that freely accessible drive components are always carefully screened off. Rotating shafts may cause serious injury! Switch OFF the engine before starting operations on the PTO or the PTO drive.

- PTO connections

Position of engine in the chassis

The angle at which the engine is positioned in the chassis in relation to the chassis side members, designated as: ∠ α in the opposite figure, should be:

LF45/55 and CF65 Series: ∠ α = 3.5°

CF75/85 Series: ∠ α = 4.5°

XF Series: ∠ α = 4.5°

Direction of rotation of the engines

The direction of rotation of the crankshaft of DAF and Cummins engines is always anti-clockwise, viewed looking towards the rear of the engine.